Refuse left by dyke builder (5)
I believe the answer is:
offal
'refuse' is the definition.
(thesaurus)
'left by dyke builder' is the wordplay.
'left' becomes 'l' (common abbreviation).
'by' says to put letters next to each other.
'dyke builder' becomes 'offa' (I've seen this before).
'l' after 'offa' is 'OFFAL'.
(Other definitions for offal that I've seen before include "Animal entrails and internal organs - worthless" , "Meaty waste" , "Edible internal parts" , "Trimmings of a butchered animal" , "Butcher's leftovers" .)